golden_divisors crashes when divs.size == 0

[ogoshen]

I was clearing out chart data when it crashed.
Stack trace did lead to

live-chart/src/utils.vala

Line 61 in 9d34b48

var last_div = divs.last();

Gee docs do say List.last() fails on an empty list.

My solution is then:

diff --git a/src/utils.vala b/src/utils.vala
index c964e2b..1f916e8 100644
--- a/src/utils.vala
+++ b/src/utils.vala
@@ -53,6 +53,10 @@ namespace LiveChart {
                 }
             } 
         }
+
+        if (divs.size == 0)
+            return new Gee.ArrayList<float?>();
+
         divs.sort((a, b) => {
             return a - b;
         });